Accumulation and histopathological effects of cadmium on the great pond snail Lymnaea stagnalis Linnaeus, 1758 (Gastropoda: Pulmonata)

Toxic responses of environmental concentrations of bifenthrin in larval freshwater snail Bellamya aeruginosa

Bifenthrin (BF) is ubiquitous in aquatic environments, and studies have indicated that environmental concentrations of BF could cause neurotoxicity and oxidative damage in fish and decrease the abundance of aquatic insects. However, little information is available on the toxicity of BF in freshwater benthic mollusks. Bellamya aeruginosa (B. aeruginosa) is a key benthic fauna species in aquatic ecosystems, and has extremely high economic and ecological values. In this study, larval B. aeruginosa within 24 h of birth were exposed to 0, 30 or 300 ng/L of BF for 30 days, and then the toxic effects from molecular to individual levels were comprehensively evaluated in all the three treatment groups. It was found that BF at 300 ng/L caused the mortality of snails. Furthermore, BF affected snail behaviors, evidenced by reduced crawling distance and crawling speed. The hepatopancreas of snails in the two BF exposure groups showed significant pathological changes, including increase in the number of yellow granules and occurrence of hemocyte infiltration, epithelial cell thinning, and necrosis. The levels of ROS and MDA were significantly increased after exposure to 300 ng/L BF, and the activities of two antioxidant enzymes SOD and CAT were increased significantly. GSH content decreased significantly after BF exposure, indicating the occurrence of oxidative damage in snails. Transcriptomic results showed that differentially expressed genes (DEGs) were significantly enriched in pathways related to metabolism and neurotoxicity (e.g., oxidative phosphorylation and Parkinson disease), and these results were consistent with those in individual and biochemical levels above. The study indicates that environmental concentration of BF results in decreased survival rates, sluggish behavior, histopathological lesions, oxidative damage, and transcriptomic changes in the larvae of B. aeruginosa. Thus, exposure of larval snails to BF in the wild at concentrations similar to those used in this study might have adverse consequences at the population level. These findings provide a theoretical basis for further assessing the ecological risk of BF to aquatic gastropods.

Physiological and biochemical responses of the estuarine pulmonate mud snail, Amphibola crenata, sub-chronically exposed to waterborne cadmium

Physiological and biochemical responses of the pulmonate mud snail, Amphibola crenata, to waterborne cadmium (Cd) were investigated to determine the mechanisms of toxicity and impacts of a 21-d Cd exposure. Mud snails were exposed to nominal Cd concentrations of 0, 0.2, 4 and 8 mg L ^- 1 and bioaccumulation, whole animal physiological (oxygen consumption, ammonia excretion and oxygen:nitrogen), and tissue level biochemical (catalase activity, lipid peroxidation, glycogen, glucose and protein) endpoints were measured every 7 days. At the two highest Cd exposure concentrations complete mortality was observed over 21-d. In surviving animals, oxygen consumption declined and ammonia excretion rate increased with Cd exposure concentration and duration. The increased ammonia excretion likely reflected enhanced protein metabolism as suggested by a reduced oxygen:nitrogen (O:N). Increasing waterborne Cd concentration and exposure time led to increasing metal accumulation in all tissues. The snail viscera showed the highest Cd accumulation. Both catalase activity and lipid peroxidation in the viscera significantly increased with Cd exposure concentration and time, whereas, the foot muscle and remaining tissues (kidney, mantle, remaining digestive tissues and heart) showed increased catalase activity and lipid peroxidation at higher Cd concentrations (4 and 8 mg L ^- 1), suggestive of an effect of Cd on oxidative stress. Over the course of 21 days, Cd exposure resulted in significantly lower levels of glycogen in viscera relative to Cd-free controls, reflecting an increased energy demand. Haemolymph glucose rose initially and then fell with increased exposure duration, while haemolymph protein generally exhibited an increased concentration in Cd-exposure groups, reflecting the changes in energy substrates noted for somatic tissues. These results suggest that the physiological and biochemical responses of A. crenata to Cd are conserved relative to other aquatic animals, and were tissue-specific, dose- and time-dependant.

Sublethal cadmium exposure in the freshwater snail Lymnaea stagnalis meets a deficient, poorly responsive metallothionein system while evoking oxidative and cellular stress

The Great Pond snail Lymnaea stagnalis (Gastropoda, Hygrophila) is a wide-spread freshwater gastropod, being considered as a model organism for research in many fields of biology, including ecotoxicology. The aim of the present study was to explore the Cd sensitivity of L. stagnalis through the measurement of a biomarker battery for oxidative, toxic and cellular stress. The interpretation of biomarker parameters occurred against the background of a truncated metallothionein protein with a limited Cd-binding capacity. Individuals of L. stagnalis were exposed through 14 days to uncontaminated water (controls) or to low (30 μg · L^-1) or high (50 μg · L^-1) Cd concentrations. The digestive gland of control and low-Cd exposed snails was processed for transcriptional analysis of the Metallothionein (MT) gene expression, and for determination of biomarkers for oxidative stress, toxicity and cellular stress. Digestive gland supernatants of high-Cd exposed snails were subjected to chromatography and subsequent analysis by spectrophotometry. It was shown that the MT system of L. stagnalis is functionally deficient, with a poor Cd responsiveness at both, the transcriptional and the protein expression levels. Instead, L. stagnalis appears to rely on alternative detoxification mechanisms such as Cd binding by phytochelatins and metal inactivation by compartmentalization within the lysosomal system. In spite of this, however, traces of Cd apparently leak out of the pre-determined detoxification pathways, leading to adverse effects, which is clearly indicated by biomarkers of oxidative and cellular stress.

Towards a Sustainable World: Diversity of Freshwater Gastropods in Relation to Environmental Factors—A Case in the Konya Closed Basin, Türkiye

The Konya Closed Basin (KCB) in Türkiye plays a key role in agricultural production and freshwater supply. However, the basin is impacted by humanly derived nitrogenous compounds and toxic metals. Keeping the water quality at a potable level in the basin is compulsory. This study was part of a project yielding monitoring of water quality in KCB in accordance with the Water Framework Directive (2000/60/EC). Eleven stations, except Beyşehir Lake and Mamasın Dam, were sampled for the first time for freshwater molluscs. Community structure indexes and multivariate statistical analyses were applied to determine the microhabitats of gastropods and their responses to environmental changes. The structure and distribution of gastropod assemblages differed depending on total phosphate, total nitrogen, dissolved oxygen, and pH. This study revealed that most of the gastropods in KCB are relatively tolerant to biodegradable pollution. However, there is a strong observed decline in population size requiring intensive future monitoring; measures have to be taken to preserve the remaining populations. Two endemic species need an urgent action plan to protect their habitats: Theodoxus anatolicus of Çeltik Canal and Bithynia pseudemmericia of Beyşehir Lake; a re-assessment of their extinction risk according to the IUCN rules is needed (2022). The results of this study will be useful for comparison with future studies to document potential improvements or continued ecological regression in the quality of aquatic ecosystems in the watershed.